A misplaced click, an unwanted transformation, or an edit that changes a structure more than expected can interrupt molecular modeling work. The first instinct is often to press Undo repeatedly—but before doing that, it helps to know what SAMSON’s history records, how to inspect it, and where its limits are.
Each SAMSON document has its own history: a list of undoable actions performed in that document. The History view lets you move through document states and see the actions that led to them. This makes it useful not only for reversing a recent change, but also for finding the point in an editing session when the structure looked the way you intended.
Open the history before guessing
Open the History view from Interface > History. You can also use Ctrl+3 on Windows or Linux, or Cmd+3 on Mac. Once it is visible, click an action in the list to move through the document’s history. This can be more deliberate than pressing Undo over and over: you can inspect the sequence of actions and choose a point to return to.
The animation below shows the idea of moving through the history. Think of the list as a record of document states—not as a guarantee that every operation in your session can be reversed.
Undo and redo when you know what changed
For a quick correction, use Edit > Undo, or press Ctrl+Z on Windows or Linux and Cmd+Z on Mac. If you undo one step too many, use Edit > Redo, Ctrl+Y on Windows or Linux, or Cmd+Y on Mac. These commands are helpful for small, recent changes; the History view is useful when you need to orient yourself among several actions.
A practical habit is to pause after an unexpected result and check the action history before continuing. Identify the operation that preceded the change, then move back only as far as needed. If the result is still unclear, avoid piling on more edits while trying to correct it: additional actions can make it harder to understand which state you want to recover.
Know the important limitation
Not every operation is undoable. The documentation also warns that when non-undoable operations occur between undoable ones, SAMSON may not be able to undo the sequence properly, which can result in data loss. So Undo is not a substitute for caution, and the history should not be treated as a complete record of every possible change.
If you are experimenting with edits, building a molecule, or testing transformations, make a habit of checking the history when something goes wrong rather than assuming every step can be reversed. Remember that each document has its own history: the action list belongs to the document you are working in.
For the full instructions and related guidance, see the SAMSON History: Undo and redo documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.